Lithographic techniques are widely used in industry to produce integrated circuit patterns in microelectronic devices such as integrated circuit chips, circuit boards and the like.
Commercially available lithographic positive, radiation-sensitive resist compositions generally contain a film-forming organic material and an o-naphthoquinone diazide which decomposes on exposure to radiation to form an indenecarboxylic acid. The film-forming organic material is usually an alkali-soluble phenol-formaldehyde novolac resin. Its dissolution in an aqueous alkaline solution is inhibited by the naphthoquinone diazide. However, when this diazide is decomposed in the irradiated areas, its efficacy as dissolution rate inhibitor decreases and the exposed areas or the coating become more soluble in a basic developer than the unexposed areas. However, the quinonediazides are not entirely satisfactory, due to their thermal instability. They decompose at moderately elevated temperatures to become unsuitable as dissolution inhibitors. Further, during normal use, the differential solubility between the exposed and the unexposed areas of the film is not high enough for certain applications. Reichmanis et al., "Chemical Amplification Mechanisms for Microlithography Chem. Mater. 3, 394 (1991), discloses the use of the tert-butyl ester of cholic acid as a dissolution inhibitor for phenol-formaldehyde matrix resin. The ester is formulated with a photoacid generator in the resin. Upon exposure to radiation, cholic acid is formed in the exposed areas making these areas more soluble in aqueous base. However, again, the differential solubility between the exposed and unexposed areas of the film is not high enough for certain applications.
It is therefore an object of the present invention to provide a radiation sensitive resist composition which has improved post-exposure differential solubility.
Other objects and advantages will become apparent from the following disclosure.